linux-kernel - [PATCH 1/2] kernel/async.c: stop guarding pr

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Message-Id: <20210309151723.1907838-1-linux@rasmusvillemoes.dk>
Date:   Tue,  9 Mar 2021 16:17:22 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Tejun Heo <tj@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] kernel/async.c: stop guarding pr_debug() statements

It's currently nigh impossible to get these pr_debug()s to print
something. Being guarded by initcall_debug means one has to enable
tons of other debug output during boot, and the system_state condition
further means it's impossible to get them when loading modules later.

Also, the compiler can't know that these global conditions do not
change, so there are W=2 warnings

kernel/async.c:125:9: warning: ‘calltime’ may be used uninitialized in this function [-Wmaybe-uninitialized]
kernel/async.c:300:9: warning: ‘starttime’ may be used uninitialized in this function [-Wmaybe-uninitialized]

Make it possible, for a DYNAMIC_DEBUG kernel, to get these to print
their messages by booting with appropriate 'dyndbg="file async.c +p"'
command line argument. For a non-DYNAMIC_DEBUG kernel, pr_debug()
compiles to nothing.

This does cost doing an unconditional ktime_get() for the starttime
value, but the corresponding ktime_get for the end time can be elided
by factoring it into a function which only gets called if the printk()
arguments end up being evaluated.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---

Andrew, this one is of course on top of
https://lore.kernel.org/lkml/20210226124355.2503524-1-linux@rasmusvillemoes.dk/
which you already applied.

 kernel/async.c | 48 ++++++++++++++++++++----------------------------
 1 file changed, 20 insertions(+), 28 deletions(-)

diff --git a/kernel/async.c b/kernel/async.c
index 45a867b8644a..4b5971142922 100644
--- a/kernel/async.c
+++ b/kernel/async.c
@@ -78,6 +78,12 @@ static DECLARE_WAIT_QUEUE_HEAD(async_done);
 
 static atomic_t entry_count;
 
+static long long microseconds_since(ktime_t start)
+{
+	ktime_t now = ktime_get();
+	return ktime_to_ns(ktime_sub(now, start)) >> 10;
+}
+
 static async_cookie_t lowest_in_progress(struct async_domain *domain)
 {
 	struct async_entry *first = NULL;
@@ -111,24 +117,18 @@ static void async_run_entry_fn(struct work_struct *work)
 	struct async_entry *entry =
 		container_of(work, struct async_entry, work);
 	unsigned long flags;
-	ktime_t calltime, delta, rettime;
+	ktime_t calltime;
 
 	/* 1) run (and print duration) */
-	if (initcall_debug && system_state < SYSTEM_RUNNING) {
-		pr_debug("calling  %lli_%pS @ %i\n",
-			(long long)entry->cookie,
-			entry->func, task_pid_nr(current));
-		calltime = ktime_get();
-	}
+	pr_debug("calling  %lli_%pS @ %i\n", (long long)entry->cookie,
+		 entry->func, task_pid_nr(current));
+	calltime = ktime_get();
+
 	entry->func(entry->data, entry->cookie);
-	if (initcall_debug && system_state < SYSTEM_RUNNING) {
-		rettime = ktime_get();
-		delta = ktime_sub(rettime, calltime);
-		pr_debug("initcall %lli_%pS returned after %lld usecs\n",
-			(long long)entry->cookie,
-			entry->func,
-			(long long)ktime_to_ns(delta) >> 10);
-	}
+
+	pr_debug("initcall %lli_%pS returned after %lld usecs\n",
+		 (long long)entry->cookie, entry->func,
+		 microseconds_since(calltime));
 
 	/* 2) remove self from the pending queues */
 	spin_lock_irqsave(&async_lock, flags);
@@ -287,23 +287,15 @@ EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
  */
 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 {
-	ktime_t starttime, delta, endtime;
+	ktime_t starttime;
 
-	if (initcall_debug && system_state < SYSTEM_RUNNING) {
-		pr_debug("async_waiting @ %i\n", task_pid_nr(current));
-		starttime = ktime_get();
-	}
+	pr_debug("async_waiting @ %i\n", task_pid_nr(current));
+	starttime = ktime_get();
 
 	wait_event(async_done, lowest_in_progress(domain) >= cookie);
 
-	if (initcall_debug && system_state < SYSTEM_RUNNING) {
-		endtime = ktime_get();
-		delta = ktime_sub(endtime, starttime);
-
-		pr_debug("async_continuing @ %i after %lli usec\n",
-			task_pid_nr(current),
-			(long long)ktime_to_ns(delta) >> 10);
-	}
+	pr_debug("async_continuing @ %i after %lli usec\n", task_pid_nr(current),
+		 microseconds_since(starttime));
 }
 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 
-- 
2.29.2